Emf Definition and 902 Threads

Hey guys. I was reading http://kansascity.injuryboard.com/automobile-accidents/toyota-recall-experts-point-to-electronics-electromagnetic-interference.aspx?googleid=277752". This paragraph jumped off the page to me, and I wanted to get your thoughts on how feasible it it. To me, it reads like...

Homework Statement Describe the way that the loop is facing for this value to be a maximum. What is the equation for the emf for the rotating loop? Homework Equations I don't know. The Attempt at a Solution I can't really attempt the problem without the equation. This is a...

Are these things for real? I know that most of the crystal pendant crap is fake, but what about teslar watches? Are there actual wristband/necklaces that can cancel, or shield a body from EMF? Thanks.

Can anyone point me in the right direction? I'm awful with electromagnetism.

I had 2 questions: 1. My textbook derives that the equation from lenz's and faraday's law emf = - d(N*flux)/dt = B * dA/dT where dA/dt = length * speed However, why does the N value disappear in the new equation? Also, this question is given after: 2. A metal propeller...

A charge Q at a vertex of a square and another Q on the opposite corner of the square and other two charges q each of the other vertices. If the force eletrogmanetica on Q is null which the value of Q in terms of q? There is a q such that the resultant force on 4 charges is zero? My attemp...

Homework Statement See picture for clarity. There are 2 infinite wires carrying a current i, one wire does it in the upward direction and the other wire in the downward direction. They are separated by a distance L+2d. Between them lies a circuit such that the part that moves with a velocity v...

I'm trying to wrap my mind around the concept of metals dissolving in water under different electrical potentials. For example, platinum is know to dissolve in liquid water when subjected to 0.65-1.1V. Why does this happen? I'm guessing it has something to due with water being so polar but why...

hi I am new member of this forum..Plz tell me how to use this forum & how to ask Question from other members...Plz tell me differences b/w emf & voltage,Resistance & resistivity..

A conducting rod moves with a constant velocity v in a direction perpendicular to a long, straight wire carrying a current I as shown in the figure below. Find the EMF It should equal U_o*V*L*I/2*pi*r, but how do I get there?

-ve sign in expression of "induced emf" What is the concept behind putting negative sign in: e=[SIZE="2"]-[rate of change of flux] Which direction does it signify?? How does direction affect the equation? How and where can we use negative sign in other expressions of induced emf??

Homework Statement A 3 m long large coil with a radius of 15.7 cm and 130 turns surrounds a 7.2 m long solenoid with a radius of 5.7 cm and 4700 turns. The current in the solenoid changes as I=I_0 sin (2\pi f t) where I0= 30 A and f=60 Hz.Inside solenoid has 4700 turns and outside coil has...

Homework Statement A flat loop of wire of area 15.7 cm2 and 1.09 turns is perpendicular to a magnetic field whose magnitude decays in time according to B = 0.5 e−t/7. What is the maximum induced emf? Answer in units of V. Homework Equations \epsilon= \Delta\PhiB/\Deltat \epsilon=...

Basically I have been given this question: A battery of unknown EMF and internal resistance is connected in series with an ammeter and a resistance box. The current was 2.0A when R= 4.0 Ohms and 1.5A when R= 6.0 Ohms. Calculate the EMF and internal resistance. I feel you may have to...

This is not a homework problem due. It's practice. I have the answer of .198mV. I don't know how to get it. Homework Statement Homework Equations \phi_b = \int \vec B \cdot d\vec A E = -\frac{d\phi_b}{dt} The Attempt at a Solution The magnetic field due to the solenoid is...

Homework Statement A solenoid of length 3.7 cm and diameter 0.95 cm is wound with 160 turns per cm. The current is decreasing at a rate of 38.0 A/s. (a) What is the induced emf in one of the windings? (b) What is the induced emf in the entire solenoid? Homework Equations emf =...

Homework Statement A circular coil with 35 turns of wire and a diameter of 19 cm is placed in a magnetic field given by B(t) = 6 t^2 + 6 t + 2 T where t is time in seconds. The field is perpendicular to the plane of the coil. What is the induced EMF at t = 5 s? Homework EquationsE=-d(magnetic...

Homework Statement A battery has an emf E and an internal resistance r. IT is connected to an external resistor R. When R=4 ohms, the potential difference is 9.5 V. When R = 6 ohms, the potential difference is 10.0 V Homework Equations The Attempt at a Solution Rtotal = R + r I =...

Homework Statement Need to draw a graph of the emf generated by a simple single-phase generator which has a coil of 200 turns. The coil is 14cm long and 9cm wide. The magnetic field in the generator is 0.15T. The generator coil is turned at a rate of 3000 revolutions per minute. Can someone...

Homework Statement Which one will produce e.m.f? (i) A circular coil placed in a non-homogenous magnetic field (ii) A circular coil moved with constant velocity in a homogenous magnetic field (iii) A circular coil moved with constant velocity in a non-homogenous magnetic field (iv) None of...

Does the emf of a battery remain its specified value for a long time. It is under discharging when connected to the external resistor, so shouldn't its emf value continuously decrease in that case? A battery's emf value increases from 0(completely discharged state) to the specified value...

Homework Statement A magnetic field is perpendicular to the plane of a single turn circular coil. The magnitude of the field is changing so that the emf of 0.80 V and a current of 3.2 A are induced in the coil. The wire is then re-formed into a single turn square coil, which is used in the...

[b]1. Derive an equation to find the induced EMF on an inner solenoid by a changing current on an outer solenoid. Homework Equations We're given the equation EoRMS=(No*Ai*(2*pi*f)*(permeability constant)*IiRMS)/Li for the induced EMF on the outer solenoid by a changing current in the...

Homework Statement A spacecraft is in a circular orbit of radius 3.1 X 10^4 km around a 1.9 X 10^30 kg pulsar. The magnetic field of the pulsar at that radial distance is 1.4 X 10^2 T directed perpendicular to the velocity of the spacecraft . The spacecraft is 0.20 km long with a radius...

Homework Statement A rectangular coil of 200 turns has a length of 200 mm and width 120 mm. The coil rotates with a constant angular speed of 1200 revolutions per minute about an axis through the midpoints of its longer sides in a uniform magnetic field of 2.4 x 10-2 T. Starting from a...

Homework Statement Hi, I found the following example in a high school physics book about electrical circuits. There's something about the example that I don't get, so I hope you can help me out. I give you the example text and the solution, and then I explain what I don't understand...

Homework Statement This is the solution to one of the problems I came across: In an AC generator, a coil spins in a magnetic field. Of the following choices, circle the one that will not cause an increase in the EMF generated in the coil? a. replacing the coil wire with one of lower...

Homework Statement two identical cells of emf E and internal resistance r are connected in series. a 7 ohm resistor is connected across the combination and draws a current of 0.333A. the two cells are now connected in parallel; the 7 ohm resistor now draws a current of 0.375A from the...

Does a single isolated charge have an electric field?

Homework Statement An AM Radio station broadcasts isotropically(equally in all directions) with an average power of 4.00kW. A dipole receiving antenna 65.0cm long is at a location 4.00 mi from the transmitter. Compute the amplitude of the emf that is induced by this signal between the ends of...

Homework Statement S is a disk of Area 0.003m2, B is a magnetic field perpendicular to S and increasing at 0.02 T per second. What is the EMF in the perimeter of S? Homework Equations I assume we need a formula relating Area, B and emf - Faraday's law of induction? or possibly phi =...

If there is electromagnetic induction on an object that has no resistance, will an emf be produced? I know that no current would flow but is emf produced? Thanks.

Ok, now I got another question while doing electromagnetic induction questions. I know flux linkage=NBA and in a rotating coil, Flux linkage=NBA cos wt, which differentiated (Faraday's Law) wrt time gives E=NBAw sin wt, where w = angular frequency. However, when the plane of the coil is...

My doubt is that when we charge a battery we say that energy is transferred into it , but does the emf of a battery change in this process ? Is the emf same before and after charging , if yes then what actually happens during charging a battery ?? pls help !

1. A 50 g horizontal metal bar, 12 cm long, is free to slide up and down between two tall, vertical metal rods. A 0.060 T magnetic field is directed perpendicular to the plane of the rods. The bar is raised to near the top of the rods, and a 1.0 Ohm resistor is connected across the two rods at...

please elaborate the difference between emf and voltage.

Homework Statement 1. A 109.3 mH inductor whose windings have a resistance of 3.6 Ω is connected across a 11 V battery having an internal resistance of 1.83 Ω. How much energy is stored in the inductor? 2. The maximum allowable potential difference across a 225.7 mH inductor is 401...

Homework Statement a tightly wound circular coil has 36.8 turns, each of radius .1m. the uniform magnetic field is in a direction perpendicular to the plane of the coil. the field increased linearly from 0 to .42t in a time of .251s. what is the emf induced in the windings of the coil...

(Solved.) 2 Unknown Currents, 1 Unknown emf, and a little confusion to boot! First off, hello everyone! I just formally joined the forums today after reading discussions from the shadows for a while now. This summer I'm taking the second part of a 200 level physics course and the...

Homework Statement A solid conductor travels at 150 m/s across a uniform .045T magnetic field. Which side is positively charged and what is the emf across this block? Homework Equations I actually solved for the emf no problem. I am having difficulty determining which side is...

1. Is there an electric motor of any type that does not produce back emf. 2. Is it possible to design a motor that does not generate back emf. 3.What are the demerits of designing a motor that do not produce back emf. 4. What are the merits of having a motor that generate back emf. 5...

What causes the back emf in motors (brushless DC motors to be exact). First thing is the rotating magnetic field of the rotor, which cuts the stator coils inducing an emf in the opposite direction. This would increase as speed increases. This is just a generator. Second, what about self...

Graph to show the variation of the p.d. V across the battery with current I as R is varied. i) Draw line of best fit. ii) Use it to determine the emf of the battery; and the internal resistance r of the battery. The gradient \approx \frac{\Delta V}{\Delta I} = 1.67 \Omega...

heres the question: A 110 turn coil has a radius of 4.1 cm and a resistance of 25 Ohm. The coil is in a uniform magnetic field that is perpendicular to the plane of the coil. What rate of change of the magnetic field strength will induce a current of 4.3 A in the coil? What rate of change of...

Homework Statement A 5.60ohm resistor is connected to a battery that has 0.200ohm internal resistance, and a terminal voltage of the battery is 10.0V. What is the current in the resistor? What is the emf of the battery? Homework Equations EMF=terminal voltage+(I)(Rint.) V=RI The...

Homework Statement A battery supplies a steady current of 5.6 A for 21s. During this time 1410J of chemical energy is transformed into electric energy, but 560J of this electric energy is transformed into heat energy inside the battery. a) What is the emf of the battery? b) What is the...

Homework Statement Im currently in my last year of high school, and I'm writing a report on AC generators. I've heard a number of different things from different sources. When the coil is perpendicular to the magnetic field, maximum magnetic flux is flowing through the coil. This is then at a...

A small loop of area A is placed inside a long solenoid that has n turns per meter and carries a sinusoidally varying current of amplitude i. The central axes of the loop and solenoid coincide. If i = i0sin ωt, find the emf in the loop. EMFinduced = - d(\phiB)/ dt \phiB=BA Bsolenoid=...

What is the difference between an induced emf and a back emf? (i) i thought they were the same thing? . . .. .